This kind of snow removing machine employs a system of changing the height of an auger according to situations in snow removing operations. When the snow removing machine is moved, the bottom of the auger is raised so that it can be moved more efficiently. On the other hand, when snow is removed, the bottom of the auger is lowered so that snow can be removed more efficiently. Also, when snow is removed, the height of the auger is changed often in accordance with bumps and dips in the road surface. It is a great burden on an operator to change the height of the auger like this manually.
In some snow removing machines, augers are vertically moved by motive power to reduce the burden on an operator. An example of such snow removing machines is known from, for example, JP-4-194109A.
The conventional auger-type snow removing machine will now be described with reference to FIG. 9 hereof.
FIG. 9 is a side elevational view of the conventional auger-type snow removing machine. The removing machine 200 is a self-propelled-type working vehicle which includes a machine body 204 provided with an auger housing 203, and a travel frame 202 provided with crawlers 201, the machine body 204 being mounted vertically movably to the travel frame 202. The machine body 204 also has a front portion vertically movable by a vertical movement adjusting device 205. The auger housing 203 is provided with an auger 206.
The body 204 and the auger housing 203 can be moved vertically by moving, forward and rearward, an auger control lever 208 provided at a steering unit 207 and telescopically moving the vertical movement adjusting device 205 through a control unit (not shown). The vertical movement adjusting device 205 comprises a cylinder device.
When a cylinder device is employed for the vertical movement adjusting device 205, a drive source for driving a cylinder is required. If a hydraulic cylinder is employed, for example, a hydraulic system disposed separately is provided in addition to the hydraulic cylinder, leading to a large size. In particular, when the snow removing machine 200 is small, employing a hydraulic cylinder is disadvantageous in terms of cylinder layout space.
To make the vertical movement adjusting device 205 small, an electrohydraulic cylinder may be employed. The electrohydraulic cylinder comprises a cylinder in which a piston telescopically moves by a hydraulic pressure generated by an electric motor, and is relatively small because an electric motor and a hydraulic system are fitted in a cylinder. A control switch is turned on and off to control the electric motor such that the piston telescopically moves to thereby move the auger 206 vertically.
When snow is removed, the height of the auger housing 203 is changed often in accordance with bumps and dips in a road surface 209, and thus the electrohydraulic cylinder is operated frequently. This causes a great load on the electric motor, and develops heating in the motor. To deal with this, it may be considered to employ a continuous-duty electric motor, which is, however, expensive and becomes a factor of a cost increase in the snow removing machine.
Given this, it is conceived to provide a thermo-breaker for protection against overheat of the motor. When the heat in the motor is developed to a temperature above a certain level, a thermo-breaker included in the electric motor breaks an energized circuit to the motor.
However, since the thermo-breaker operated does not recover the energized circuit until the heat is lowered, recovery takes time. If a set operation temperature of the thermo-breaker is set low, the energized circuit to the motor is broken frequently. If a set operation temperature of the thermo-breaker is set high, the frequency of breaking is reduced, but a recovery time after breaking is long. To enable a more smooth snow removing operation, it is desirable to reduce the frequency of operation of the thermo-breaker.